This invention relates to the field of sorbent compositions.
This invention relates to the field of particulate compositions.
Fluidized bed reactors have advantages over fixed bed reactors such as better heat transfer and better pressure drop. Fluidized bed reactors generally use reactants that are particulates. The size of these particulates is generally in the range of about 1 to about 1000 microns. However, the reactants used generally do not have sufficient thermal stability and sufficient attrition resistance for all applications.
The removal of sulfur from fluid streams has long been desirable, as well as necessary, for a variety of reasons. If a sulfur-containing-fluid-stream is to be released as a waste stream, removal of such sulfur from the fluid stream is often necessary to meet certain environmental regulations. If a sulfur-containing-fluid-stream is to be used in a catalytic process, removal of such sulfur is often necessary to prevent catalyst poisoning. Sulfur-containing-fluid-streams are sometimes used in fluidized bed reactors. Fluidized bed reactors have advantages over fixed bed reactors such as better heat transfer and better pressure drop. Fluidized bed reactors generally use reactants that are particulates. The size of these particulates is generally in the range of about 1 to about 1000 microns. However, the reactants used generally do not have sufficient thermal stability and sufficient attrition resistance for all applications. Consequently, finding a sorbent that removes sulfur from these fluid streams and that can be used in fluidized bed reactors is desirable.
It is an object of this invention to provide a process to produce a particulate composition.
It is another object of this invention to provide a process to produce a particulate composition that has improved thermal stability and improved attrition resistance and that can be used in a wide variety of applications.
In accordance with this invention a process is provided to produce a particulate composition that comprises zinc aluminate. This process comprises: (a) contacting a zinc component, an alumina component, a dispersant component, to form a mixture, and the (b) spray drying said mixture to form said particulate composition.
It is an object of this invention to provide a process to produce a sorbent composition.
It is another object of this invention to provide a process to produce a sorbent composition that has improved thermal stability and improved attrition resistance and that can be used in fluidized bed reactors.
In accordance with this invention a process is provided to produce a sorbent composition. This process comprises: (a) contacting a zinc component, an alumina component, and a dispersant component, to form a mixture; and then (b) spray drying said mixture to form particles; and then (c) contacting said particles with a zinc compound, wherein said zinc compound is zinc oxide, or it is a compound convertible to zinc oxide, to form a sorbent composition.
Generally, the zinc component is zinc oxide. However, it may be any zinc compound that combines with alumina to form zinc aluminate under the conditions of preparation described herein. Examples of such compounds include, but are not limited to, zinc sulfide, zinc sulfate, zinc hydroxide, zinc carbonate, zinc acetate, zinc nitrate, zinc chloride, zinc bromide, zinc iodide, zinc oxychloride, and zinc stearate. Mixtures of such compounds can also be used. The amount of the zinc component used is in the range of about 5 to about 75 weight percent based on the total weight of the components. However, an amount in the range of about 15 to about 60 weight percent is preferred and an amount in the range of about 25 to about 45 weight percent is most preferred.
The alumina component can be any suitable alumina or aluminosilicate. The alumina component should combine with the zinc component, under the conditions of preparation herein, to form zinc aluminate. Suitable alumina components include, but are not limited to, hydrated alumina and flame-hydrolyzed alumina. The amount of the alumina component used is in the range of about 5 to about 90 weight percent based on the total weight of the components. However, an amount in the range of about 25 to about 75 weight percent is preferred and an amount in the range of about 40 to about 65 weight percent is most preferred.
The dispersant component can be any suitable compound that helps to promote the spray drying ability of the mixture. In particular, these components are useful in preventing deposition, precipitation, settling, agglomerating, adhering, and caking of solid particles in a fluid medium. Suitable dispersants include, but are not limited to, condensed phosphates and sulfonated polymers. The term condensed phosphates refers to any dehydrated phosphate where the H2O:P2O5 is less than about 3:1. Specific examples of suitable dispersants include, but are not limited to, sodium pyrophosphate, sodium metaphosphate, and sulfonated styrene maleic anhydride polymer. The amount of the component used is in the range of about 0.01 to about 10 weight percent based on the total weight of the components. However, an amount in the range of about 0.1 to about 8 weight percent is preferred and an amount in the range of about 1 to about 3 weight percent is most preferred.
In a preferred embodiment of the invention a binder component is used. The binder component can be any suitable compound that has cement-like properties, or clay-like properties, which can help to bind the particulate composition together. Suitable examples of such binder components include, but are not limited to, cements such as, for example, gypsum plaster, common lime, hydraulic lime, natural cements, portland cements, and high alumina cements, and clays, such as, for example, attapulgite, bentonite, halloysite, hectorite, kaolinite, montmorillonite, pyrophylite, sepiolite, talc, and vermiculite. A particularly preferred binder component is calcium aluminate cement. The amount of binder component used is in the range of about 0.1 to about 30 weight percent based on the total weight of the components. However, an amount in the range of about 1 to about 20 weight percent is preferred and an amount in the range of about 5 to about 15 weight percent is most preferred.
In another preferred embodiment of the invention an acid component is used. The acid component can be any suitable acid that can help form zinc aluminate from the zinc component and the alumina component. In general, the acid component can be an organic acid or a mineral acid. If the acid component is an organic acid it is preferred if it is a carboxylic acid. If the acid component is a mineral acid preferably it is a nitric acid, a phosphoric acid, or a sulfuiric acid. Mixtures of these acids can also be used. Generally, the acid is used with water to form a dilute aqueous acid solution. The amount of acid in the acid component is in the range of about 0.01 to about 20 volume percent based on the total volume of the acid component. However, it is preferred if the amount is in the range of about 0.1 to 10 volume percent and it is most preferred if the amount is in the range of about 1 to about 5 volume percent. In general, the amount of acid component to use is based on the amount the dry components. That is, the ratio of all the dry components (in grams) to the acid component (in milliliters) should be less than about 1.75:1. However, it is preferred if this ratio is less than about 1.25:1 and it is more preferred if it is less than about 0.75:1. These ratios will help to form a mixture that is a liquid solution, a slurry, or a paste that is capable of being dispersed in a fluid like spray.
The zinc component, alumina component, and dispersant component can be contacted together in any manner known in the art that will form a mixture that is a liquid solution, a slurry, or a paste that is capable of being dispersed in a fluid like spray. When the zinc component, alumina component, and dispersant component are solids then they should be contacted in a liquid medium to form a mixture that is a liquid solution, a slurry, or a paste that is capable of being dispersed in a fluid like spray. In another embodiment of the invention, the zinc component and the alumina component can be contacted together to form a composition comprising zinc aluminate and then this zinc aluminate composition is contacted with a dispersant. Suitable means for contacting these components are known in the art such as, for example, tumblers, stationary shells, troughs, muller mixers, impact mixers, and the like. If desired, a binder component can be contacted with the other components to form, among other things, a composition that has improved attrition resistance. Generally, these components, after contacting to form a mixture, are contacted with the acid component. However, the dry components and the acid components can be contacted together simultaneously or separately. The ratio of all the dry components (in grams) to the components that are liquids (in milliliters) should be less than about 1.75:1. However, it is preferred if this ratio is less than about 1.25:1 and it is more preferred if it is less than about 0.75:1. These ratios will help to form a mixture that is a liquid solution, a slurry, or a paste that is capable of being dispersed in a fluid like spray.
After the components are contacted together to form a mixture, they are subjected to spray drying to form a particulate composition having particles that have a size from about 1 to about 1000 microns. Spray drying is known in and art and is discussed in PERRY""S CHEMICAL ENGINEERS"" HANDBOOK, sixth edition, published by McGraw-Hill, Inc. at pages 20-54 through 20-58. Additional information can be obtained, especially from the bibliography, from the HANDBOOK OF INDUSTRIAL DRYING, published by Marcel Dekker. Inc. pages 243 through 293. The particulate compositions formed can have a size from about 10 to about 1000 microns. However, it is preferred if the size of the particles is from about 30 to about 300 and it is most preferred if the size is from about 50 to about 100 microns.
The dried, particulate composition can then be calcined to form a calcined, particulate composition. The calcination can be conducted under any suitable conditions that remove residual water, oxidize any combustibles, and effect the combination of the zinc component and the alumina component to form zinc aluminate. Usually, the dried composition is then calcined in an oxygen containing ambient. Generally, the temperature that the calcination takes place at is in the range of about 300 to about 1200xc2x0 C. However, it is more preferred if the temperature is in the range of about 450 to about 1000xc2x0 C. The calcination should be conducted for a period of time in the range of about 0.5 to about 12 hours.
After the dried particulate composition is formed, or after the calcined, dried particulate composition is formed, it can be contacted with zinc compound. Generally, the zinc compound is zinc oxide. However, it may be any zinc compound that is convertible to zinc oxide under the conditions of preparation herein. Examples of such compounds include, but are not limited to, zinc sulfide, zinc sulfate, zinc hydroxide, zinc carbonate, zinc acetate, zinc nitrate, zinc chloride, zinc bromide, zinc iodide, zinc oxychloride, and zinc stearate. Mixtures of such compounds can also be used. The amount of the zinc compound used is in the range of about 5 to about 75 weight percent based on the total weight of the components. However, an amount in the range of about 15 to about 60 weight percent is preferred and an amount in the range of about 25 to about 45 weight percent is most preferred. In a preferred embodiment, the dried particulate composition, or the calcined, dried particulate composition can be contacted with a liquid medium that comprises a soluble zinc compound. Generally, the soluble zinc compound is a compound that is convertible to zinc oxide during the preparation of the sorbent composition. The liquid medium can be any medium such as, for example, water and organic solvents. Examples of soluble zinc compounds include, but are not limited to, zinc sulfide, zinc sulfate, zinc carbonate, zinc acetate, zinc nitrate, zinc chloride, zinc bromide, and zinc iodide. Mixtures of these soluble zinc compounds can also be used.
The liquid medium that comprises the soluble zinc compound can be contacted with the particulate composition in any manner known in the art. One such method is the impregnation of the particulate composition with the liquid medium. After the particulate composition has been mixed with the liquid medium that comprises the soluble zinc compound, the composition is dried and calcined. This composition is preferably dried at a temperature in the range of about 50xc2x0 C. to about 300xc2x0 C., but more preferably, the drying temperature will range from about 100xc2x0 C. to about 250xc2x0 C., for a period of time in the range of about 0.5 hour to about 8 hours, more preferably in the range of about 1 hours to about 5 hours. This dried composition is then calcined in the presence of oxygen, or an oxygen-containing gas, at a temperature in the range of about 300xc2x0 C. to about 800xc2x0 C., and more preferably in the range of about 450xc2x0 C. to about 750xc2x0 C., to remove residual water, oxidize any combustibles, and effect the conversion of at least a portion of the zinc compound to zinc oxide. The time required for this calcining step will generally be in the range of about 0.5 hour to about 4 hours, and will preferably be in the range of about 1 hour to about 3 hours.
If desired, a metal oxide component can be added to the composition. These metal oxide components can improve the physical and chemical properties of the sorbent composition. For example, these metal oxide components can increase the ability of the sorbent composition to hydrogenate various compounds. Examples of suitable metal oxide components include, but are not limited to, iron oxide, cobalt oxide, nickel oxide, ruthenium oxide, rhodium oxide, palladium oxide, osmium oxide, iridium oxide, platinum oxide, copper oxide, chromium oxide, titanium oxide, zirconium oxide, tin oxide, and manganese oxide. The amount of metal oxide component in the sorbent composition is in the range of about 0.01 to about 20 weight percent based on the weight of the sorbent composition. However, it is more preferable if the amount is in the range of about 0.1 to about 15 weight percent, and most preferably the amount is in the range of about 1 to about 10 weight percent.
The metal oxide component can be added to the sorbent composition in the form of the elemental metal, metal oxide, and/or metal-containing compounds that are convertible to metal oxides under the calcining conditions described herein. Some examples of such metal-containing compounds include metal acetates, metal carbonates, metal nitrates, metal sulfates, metal thiocyanates and mixtures of any two or more thereof.
The elemental metal, metal oxide, and/or metal-containing compounds can be added to the sorbent composition by any method known in the art. One such method is the impregnation of the sorbent composition with a liquid medium, either aqueous or organic, that contains the elemental metal, metal oxide, and/or metal-containing compounds. After the elemental metal, metal oxide, and/or metal-containing compounds have been added to the sorbent composition, the composition is dried and calcined.
The elemental metal, metal oxide, and/or metal-containing compounds can be added to the particulate composition as components of the original mixture, or they can be added after the particulate composition has been spray dried and calcined, or after the soluble zinc compound has been added to the particulate composition and dried and calcine. If the metal oxide is added to the particulate composition after it has been spray dried and calcined, or if the metal oxide is added to the sorbent composition after it has been dried and calcined, the composition should be dried and calcined a second time. This composition is preferably dried at a temperature in the range of about 50xc2x0 C. to about 300xc2x0 C., but more preferably, the drying temperature will range from about 100xc2x0 C. to about 250xc2x0 C., for a period of time in the range of about 0.5 hour to about 8 hours, more preferably in the range of about 1 hours to about 5 hours. This dried composition is then calcined in the presence of oxygen, or an oxygen-containing gas, at a temperature in the range of about 300xc2x0 C. to about 800xc2x0 C., and more preferably in the range of about 450xc2x0 C. to about 750xc2x0 C., until volatile matter is removed and until at least a portion of the elemental metal and/or the metal-containing compounds is converted to a metal oxide. The time required for this calcining step will generally be in the range of about 0.5 hour to about 4 hours, and will preferably be in the range of about 1 hour to about 3 hours.
The sorbent compositions of this invention can be used in sulfur removal processes where there is achieved a contacting of the sorbent composition with a sulfur-containing gaseous feed stream, and thereafter, of the sorbent composition with oxygen or an oxygen-containing gas which is utilized to regenerate the sorbent composition. Examples of such sulfur removal processes are disclosed in U.S. Pat. Nos. 4,990,318; 5,077,261; 5,102,854; 5,108,975; 5,130,288; 5,174,919; 5,177,050; 5,219,542; 5,244,641; 5,248,481; and 5,281,445; the disclosures of which are hereby incorporated by reference.